387. First Unique Character in a String

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題目敘述

Given a string s, find the first non-repeating character in it and return its index. If it does not exist, return -1.

Example 1

Input: s = “leetcode” Output: 0

Example 2

Input: s = “loveleetcode” Output: 2

Example 3

Input: s = “aabb” Output: -1

解題思路

Solution

import java.util.HashMap;
import java.util.Map;

class Solution {
    public int firstUniqChar(String s) {
        Map<Character, Integer> map = new HashMap<>();

        for(int i = 0; i < s.length(); i++){
            map.put(s.charAt(i), map.getOrDefault(s.charAt(i), 0) + 1);
        }

        for(int i = 0; i < s.length(); i++){
            if(map.get(s.charAt(i)) == 1){
                return i;
            }
        }

        return -1;
    }
}